Numerical Simulation of the Domino Effect of Mooring System Failure for an Aquaculture Net Cage Under Waves and Currents

2020 ◽  
Author(s):  
Hung-Jie Tang ◽  
Ray-Yeng Yang ◽  
Tzu-Chieh Wen ◽  
Po-Hung Yeh ◽  
Chai-Cheng Huang
Keyword(s):  
Line Tension ◽  
Body Motion ◽  
Economic Losses ◽  
Mooring Line ◽  
Mooring System ◽  
System Failure ◽  
Domino Effect ◽  
Lumped Mass ◽  
Waves And Currents ◽  
Net Cage

Abstract Up to date, the mooring system failure of aquaculture net cage remains a continuing problem, especially the domino effect, which often leads to huge economic losses. Thus, this study aims to investigate the domino effect of a mooring system of a net cage under waves and currents. In this study, a time-domain numerical model based on the Morison equation and the lumped mass method is applied. A full-scale net cage system widely used in a local sea area is adopted. A 50 years return period waves with a strong following current is considered to be the design condition. It can be expected that the tension on the remaining upstream anchor increases dramatically when an upstream anchor is lost. Then, the domino effect occurs if the maximum tension on the remaining anchor exceeds its design condition. Therefore, in this simulation, the initial failure is considered to be a man-made event at a preset time, but the rest failures are resulted from exceeding the breaking strength of a rope. Both the current-only condition and the wave-current condition have been examined. The results including mooring line tension, volume reduction coefficient and rigid body motion are discussed. In addition, the results show that the failure sequence of anchor is different between the current-only condition and the wave-current condition.

Numerical Simulation of the Domino Effect of Mooring System Failure for an Aquaculture Net Cage Under Waves and Currents

2021 ◽  
Author(s):  
Hung-Jie Tang ◽  
Ray-Yeng Yang ◽  
Tzu-Chieh Wen ◽  
Po-Hung Yeh ◽  
Chai-Cheng Huang
Keyword(s):  
Numerical Simulation ◽  
Mooring System ◽  
System Failure ◽  
Domino Effect ◽  
Waves And Currents ◽  
Net Cage

The Dynamic Motion of the OC4 Floating Turbine with Different Incident Wave and Wind Directions in a Mooring System Failure Condition in Numerical Model

2020 ◽  
Author(s):  
Tzu-Ching Chuang ◽  
Wen-Hsuan Yang ◽  
Yi-Hong Chen ◽  
Ray-Yeng Yang
Keyword(s):  
Steady State ◽  
Line Tension ◽  
Time Domain Analysis ◽  
Mooring Line ◽  
Second Phase ◽  
Mooring System ◽  
System Failure ◽  
Floating Platform ◽  
Initial Tension ◽  
Wave Condition

<p><span>In this paper, the commercial software Orcaflex is used to simulate the motion behavior of the OC4 floating platform, and the floater stability and mooring line tension after the mooring system failure. In the time domain analysis, the discussion is divided into three phases—the first phase (before the tether failure), the second phase (before the tether failure, before reaching the new steady-state), and the third phase (after reaching the new steady-state). The motion characteristics and tension values at different stages were observed. In this study, only a 50-year return period wave condition is used as an input condition and simulating 11 different incident wind and wave directions. The numerical results are presented in the trajectory map and the table. About the tension of the mooring line, after the mooring system fails, it is notable that the mooring line tension will first decrease and then increase slightly above the initial tension value. In other words, the mooring system may survive after the failure of one mooring line and got a new balance of it. However, the tension amplitude will be higher than the first stage in the new balance and it will likely increase the risk of mooring line fatigue.</span></p>

Hydrodynamic Behaviors of Aquaculture Net Cages After the Successive Mooring Lines Failure

2021 ◽  
Author(s):  
Hung-Jie Tang ◽  
Ray-Yeng Yang
Keyword(s):  
Mooring Line ◽  
Mooring System ◽  
Domino Effect ◽  
Lumped Mass ◽  
Mooring Lines ◽  
Upstream Side ◽  
Anchor Points ◽  
The Time Domain ◽  
Net Cages ◽  
Hydrodynamic Behaviors

Abstract This paper aims to study the successive mooring line failure (also known as the domino effect) and the collision between floating collars for aquaculture net cages subjected to currents. The numerical model of this study is developed based on the Morison equation and the lumped-mass scheme in the time domain. This model is then applied to see if the domino effect of moorings will happen after releasing the anchor point #1 on the upstream side. In this study, we adopt four different current speeds (0.5, 1.0, 1.5, 2.0 m/s) and three different safety factors (SF, 1.0, 1.5, 2.0) settings to calculate the number of mooring failures, and to see whether it will cause floating collars collision. The results show that in the case of the SF is 2.0, the domino effect will not be triggered, and the floating collar collision will not occur. When the SF is 1.5, and the current speed is up to 1.0 m/s or higher, only the two anchor points on the upstream side will fail and no collision will occur. However, if the SF is not considered (that is, 1.0), the domino effect will occur under all the four current speeds, and the floating collar collision will all occur. Therefore, we suggest that in order to avoid the domino effect of the mooring system of aquaculture net cages from currents, the SF of the mooring system design must be at least 2 times.

scholarly journals Dynamic Analysis of Embedded Chains in Mooring Line for Fish Cage System

2018 ◽  
Vol 25 (4) ◽  
pp. 83-97
Author(s):  
Hui-Min Hou ◽  
Guo-Hai Dong ◽  
Tiao-Jian Xu ◽  
Yun-Peng Zhao ◽  
Chun-Wei Bi
Keyword(s):  
Numerical Model ◽  
Dynamic Response ◽  
Single Point ◽  
Mooring Line ◽  
Mooring System ◽  
Lumped Mass ◽  
Model Case ◽  
Cage System ◽  
Net Cage ◽  
Offshore Aquaculture

Abstract Investigation of the embedded chains in soil starts to play an important role in understanding the structural performance of mooring system, when the embedded anchors will be employed to sustain large loads with the gradually growth of installation depth of offshore aquaculture farm. The aim of this study is to investigate the dynamic response of mooring line considering the influence of embedded chains in clay soil for net cage system. Lumped-mass method is used to establish the numerical model for evaluating the performance of mooring line with embedded chains. To validate the numerical model, comparisons of numerical results with the analytical formulas and the experimental data are conducted. A good agreement of the profile and the tension response is obtained. Then, the effect of embedded chains on the static and dynamic response of mooring line is evaluated, and the dynamic behavior of mooring system considering embedded chains for net cage system is investigated. The results indicate that the soil resistance on embedded chains should be included to predict the mooring line development and the load on the embedded anchors in the numerical simulations. An appropriate safety factor should be included if employing the simplified model Case C at the initial design phase. And the effect of embedded chains on the holding capacity of embedded anchors in single-point mooring system for single net cage cannot be negligible during the design and operation phases. Consequently, it is profound to take into account the interaction of embedded chains and soil for accurately predicting the reliability of mooring system for fish cage.

scholarly journals On mooring line tension and fatigue prediction for offshore vertical axis wind turbines: A comparison of lumped mass and quasi-static approaches

2018 ◽  
Vol 42 (2) ◽  
pp. 97-107 ◽  
Author(s):  
D Cevasco ◽  
M Collu ◽  
CM Rizzo ◽  
M Hall
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Line Tension ◽  
Vertical Axis ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Vertical Axis Wind Turbine ◽  
Lumped Mass ◽  
Vertical Axis Wind Turbines

Despite several potential advantages, relatively few studies and design support tools have been developed for floating vertical axis wind turbines. Due to the substantial aerodynamics differences, the analyses of vertical axis wind turbine on floating structures cannot be easily extended from what have been already done for horizontal axis wind turbines. Therefore, the main aim of the present work is to compare the dynamic response of the floating offshore wind turbine system adopting two different mooring dynamics approaches. Two versions of the in-house aero-hydro-mooring coupled model of dynamics for floating vertical axis wind turbine (FloVAWT) have been used, employing a mooring quasi-static model, which solves the equations using an energetic approach, and a modified version of floating vertical axis wind turbine, which instead couples with the lumped mass mooring line model MoorDyn. The results, in terms of mooring line tension, fatigue and response in frequency have been obtained and analysed, based on a 5 MW Darrieus type rotor supported by the OC4-DeepCwind semisubmersible.

Numerical Modelling of the Mooring Line Failure Induced Performance Changes of a Marine Fish Cage in Irregular Waves and Currents

2019 ◽  
Author(s):  
Hung-Jie Tang ◽  
Ray-Yeng Yang ◽  
Chai-Cheng Huang
Keyword(s):  
Marine Fish ◽  
Low Frequency ◽  
Frequency Region ◽  
Irregular Waves ◽  
Mooring Line ◽  
Lumped Mass ◽  
Lumped Mass Method ◽  
Waves And Currents ◽  
Failure Scenario ◽  
The Time Domain

Abstract This study aims to investigate the performance changes resulted from a mooring line failure of a marine fish cage exposed to irregular waves and current. A numerical model based on the lumped mass method and Morison equation was extended to simulate the mooring line failure scenario. In this study, the failed resulting changes were compared with its normal counterpart in both the time domain and the frequency domain. After one upstream anchor loss, the maximum tension on the remaining anchor has increased significantly, as well as the drift distance of the rearing part (net chamber, floating collar, and tube-sinker) of the fish cage. The resulting changes can also be seen in both the wave-frequency and the low-frequency region in the spectra, including mooring tensions and body motions.

scholarly journals Numerical Study on Hydrodynamic Responses of Floating Rope Enclosure in Waves and Currents

2020 ◽  
Vol 8 (2) ◽  
pp. 82
Author(s):  
Hui Yang ◽  
Yun-Peng Zhao ◽  
Chun-Wei Bi ◽  
Yong Cui
Keyword(s):  
Numerical Study ◽  
Line Tension ◽  
Wave Period ◽  
Windward Side ◽  
Mooring Line ◽  
Fish Stock ◽  
Lumped Mass ◽  
Mooring Lines ◽  
Design Factors ◽  
Volume Retention

Enclosure aquaculture is a healthy and ecological aquaculture pattern developed in recent years to relieve the pressure due to the wild fish stock decline and water pollution. The object of this paper was a floating rope enclosure, which mainly consisted of floaters, mooring lines, sinkers and a net. In order to optimize mooring design factors, the hydrodynamic responses of the floating rope enclosure with different mooring systems in combined wave-current were investigated by experimental and numerical methods. Physical model experiments with a model scale of 1:50 were performed to investigate the hydrodynamic characteristics of a floating rope enclosure with 12 mooring lines. Based on the lumped mass method, the numerical model was established to investigate the effects of mooring design factors on the mooring line tension, force acting on the bottom, and the volume retention of the floating rope enclosure. Through the analysis of numerical and experimental results, it was found that the maximum mooring line tension of the floating rope enclosure occurs on both sides of the windward. Increasing the number of mooring lines on the windward side is helpful to reduce the maximum mooring line tension. Waves and current both have an influence on the mooring line tension; in contrast, currents have a more obvious effect on the mooring line tension than waves. However, the influence of the wave period on the maximum mooring line tension is small. The force endured by the bottom of the floating rope enclosure also changes periodically with the wave period. Yet, the maximum force endured by the bottom of floating rope enclosure occurred at the windward and leeward of the structure. The volume retention of the floating rope enclosure increased with the increasing amount of mooring lines.

Study on Weight Control Methods of Single Point Mooring System of FPSO in Deepwater

2015 ◽  
Author(s):  
Yuan Hongtao ◽  
Zeng Ji ◽  
Chen Gang ◽  
Mo Jian ◽  
Zhao Nan
Keyword(s):  
Weight Control ◽  
Linear Time ◽  
Single Point ◽  
Line Tension ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Mooring System ◽  
Control Methods ◽  
Analysis Method ◽  
Mooring Lines

This paper applies 3D potential theory and non-linear time domain coupled analysis method to analyze motion response of FPSO and dynamic response of mooring line of single mooring system. In addition, respectively to calculate mooring line tension of tension type and composite mooring line type and added buoy in mooring line. There the paper analyze different mooring lines to affect on the weight of single point mooring system of deepwater FPSO. Which expects to provide a theoretical basis for single point mooring system design and weight control.

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